Corrosion resistant coating for ferrous products



Patented Aug. 9, 1949 CORROSION RESISTANT COATING FOR FERROUS PRODUCTS Carl H. Hack, Flushing, Gustave E. Behr, New York, and George J. Vahrenkamp, Wood Haven, N. Y., assignors to National Lead Company,

New York, N. Y., a corporation of New Jersey No Drawing. Application July 19, 1947, Serial No. 762,198

This invention relates to corrosion resistant ferrous products and more particularly to a method for the protection of corrodible ferrous surfaces.

It is well known that some form of protection microscopic discontinuities known as pores or pin holes are always found desp te the best efforts of those skilled in the art. It has been recognized that while heavier coatings reduce porosity, pin

holes cannot be eliminated by increasing the thickness of coating metal,

It has been known that where the coating metal is of a nature more corrod ble than iron, i.e., more anodic, such as z nc or cadmium, for instance, it

v is sacrificially corroded in a galvanic couple with iron. In such conditions, pin holes are not considered to be a serious problem until the coating metal in the immediate area of the pin hole is used up. In contrast to the foregoing, where the 6 Claims. (Cl. 1486.21)

or steel by first applying thereto an adherent coating of lead or a lead alloy and subsequently chemically treating the metal coated surface with an alkaline solution .of dichromate and sulphate binations of these. 1

The chemical treatment may be accomplished preferably by immersing the leadcoated surface in the alkaline salt solution while maintaining same at'an elevated temperature. Qther methods of applying the solution may be employed if desirable or necessary, such as for instance, spraying. The solution comprises a ternary system in aqueous media of the following components:

is necessary to prevent ordinary iron and steel salts. After treatment with the alkali salt soluproducts from rusting under atmospheric as well tion the surface is dried and preferably covered as marine exposure. The art of chemical treatwith a film forming and drying coating composiment has been developed to offer temporary protion such as paint or lacquer.

tection, but more particularly to offer a .better The adherent lead or lead alloy coating maybe base forsubsequent painting or baked enamel m applied by anyconveni n method; however, i is finishing. preferable to apply this by hot dipping; The coat- Non-ferrous metal coatings such as those of ing should be uniform and m y advantageously zinc, cadmium, tin, nickel, chromium and lead be from about 0.0002 to 0.001 inch in thickness. have commonly been applied to various metal Such thickness provides sufiicientmetalfor a products by galvanic or electrolytic deposition or complete uniform film as well as for react1on by spraying or hot dipping. The ability of lead with the chemical treatment as hereinafter deand zinc to withstand atmospheric corrosion has scribed in detail. The lead coating, may, if delong been known and such coatings are usually sired, comprise pure lead or may comprise alead applied by hot dipping. In all cases of hot dip alloy for instance, containing minor amounts of coatings on iron and steel, certain numerous tin or antimony, or other a l y metals Q 1 (1) An alkali metal dichromate (2) An alkali metal sulphate (3) An alkali metal hydroxide coating metal is less corrodible than iron or steel, It is preferred from an e onomi standpoint t 'us for instance, lead or lead alloys, i. e. cathodic, no sodium dichromate NazCrzOaZHzO, sodium Sulgalvanic protection is obtained at exposed areas phate M 50 and caustic soda NaOH; however, Such as p 110165, and Cor os o may be accelpotassium or other alkali metal salts will produce era/Bed; substantially equivalent results. The solution It is therefore, a principal j ct of this ih should contain each of the component salts in tion t pro de an improved method for o ectamount from about 15% to 40% of the total solids ing corrodible ferrous 'metal surfaces. It is ant t and t concentration h d b about other object to provide a method for protect ng from 30 grams to about 120 grams. of combined corrodible ferrous metal surfaces which substansolids per liter. A commercially available W tially eliminates pin hole failure of metallic coatting agent such as a sodium sulfate derivative of ings. It is a further .object of this invention to 2-ethyl-hexanol for instance, maybe incorporated provide a method for protecting corrodible ferrous in the salt solution if desired in amou t a u metal surfaces with lead in which the corrosion more .or less. producing galvanic effect is substantially eliml- Apparently, the chemical salt solution as denated. A still further object is to provide a coatscribed above reacts to some extent or degree with ing which will protect corrodible ferrous metal the lead coated surface. It has beenfound that surfaces from corrosion. an elevatedtemperature of from about F. to

In its broadest aspects, this invention contemabout F. is advantageous; also, the immerplates protection against corrosion of normally sion time or contact period-may vary widely, for corrodible surface, such as that of ordinary iron instance, from about 10 seconds to several minforming and drying surface coating composition such as, for instance, paint or lacquer. The enhanced protection thus obtained 'is one "of the unique features of this invention and is apparently substantially greater than that normally expected from such coating. A synergistic effect on the resistance to corrosion imparted -.b y the lead coated and chemical treated surface and the top film, paint or lacquer, for instance, is definitely indicated.

In o rder that this invention may be more clearly "understood, the following examples are given:

. EXAMPLE ,1

-22 gauge cold rolled steel sheets-measuring "5%" wide and *6 long, :were subjected tozpre liminnry deer-easing with .a customary .alkaline cleaner; washing :and zpickling liIl iii-101% sulturie acid solution for lhflminutes sat about ;l50'-F., followed by washing in water. illhe isheets were ing 'machine through -a onehalf inch layer of anhydrous -=containing 80% zinc chloride --and*20% sodium chloride, waiter-which the sheet "was -passed into #the *molten alloy lbath iof arcom- "position 2% tin, 98 lead, maintained :at .a tem- *perature of between 680 F. and- 70N11 'ilhe coated sheet emerged through exit rolls ifluxed with a'layer of similar flux to keep the rolls properly tinned. The speed of'the rolls and immen sion time "tfactor "was controlled to produce :a thickness of approximately 05000 95 of lead al- "lov coating metal. "The "lead coated surface :was

'then immersed in the alkaline chemical treating bath for 30 seconds-at about 140 -removed', the excess solution allowed to drain off' and allowedeto dry in air. The composition of the chemical heating solution wa as-follows:

Grams per liter Sodium diehromate 1 8 Sodium sulfate 18 Caustic soda 24 Sodium sulfate derivative (2eetlhylehexanoL) Th EXAMPLE Ia illustrate ithfi reomleymentof a top manor ra mm :Eormi-ng and :drying surface coatin comm" .sition, .a part of the sheet steel :lead acoa-ted and zchemicallrtizeatedas in :Elxample .I was g n a mat =.of cmmnerciai lacquer arnhl -brsmuuina Gut "sections of 16 mesh iron 'fiyscreen, v6" wide and 6" long, =were degreased with .a proper commercial cleaner, washed and then pickled in a hydrochloric-acid solution at room:.tem- =peraturefor -a few minutes. =I he screening was "then fed into the entrance rolls of -a small ooat- 4 ing machine through a one-half inch layer of an: hydrous 80% zinc chloride-% sodium chloride flux, after which the screening passed into the molten alloy bath of a composition 2% tin, 98 93 dead, [maintained at a temperature of between 680 F. and 700 F. The screening emerged through exit rolls which were kept well tinned by a thin layer of similar flux contained in a flux 'LbQX and prevented from getting onto the roll 'inlp iby means of end bafiles. The coated screen was then placed in the alkaline chemical treatingsolution similarto that described in Example jI'for about30.seconds at about 140 F. and re .moveidrainedand allowed to dry in air.

EXAMPLE III It will be understood that in addition to the f errous sheet and wire mesh screening shown in Examples I and II, this invention is also adapted to the treatment. .of small ferrous .parts. A basket .of .-.c1eaned .small .parts was. immersed through a proper flux .intocmolten coating bath of 3.25 .tin, 2% antimony .leadalloy ,fora period of time and .at .a temperature ,also similar to that described in Example :1. Upon removal from the molten hath, the basket of .parts .set .in .a suitable centrifuge and reyolved .at a speed of about 500 33.. RM. which was effective in .thmw- ,ine off the flux .andexcess metal clinging to the parts. After about 5 seconds of centrifugi ,resuiting. in .a layer .of lead alloy coating metal of about .0 00ll3. inch thickness, the basket of coated parts was ,removedand dumped into runnin cold water. -.and the parts washed for ,a few minutes. jflhey were .then .immersedin the chemical .treating solution described Example 1 a similar period of .timeand at .as'iniilar temperature and .then. centrifuged to remove .excess treating .solu- .tion. anddriedin air.

.Snecimens .oflthercoldrrolled steel products of Example 1 were selected for comparative tests with .yarious forms .ofother ferrous coated mate- .liials commonly used. :Ehis'test was the standard .soll sprayftest.conductedaccording'lto themethod described in "the American Society for Testing .Materials .Standard, 1944., Part 1-'Me.tals, beginnin n page 1,843. All panels were 5%" by about 22" with outedges of exposed-steel protected in .theusual manner by reKiAlead-in-oil ,paste. Resuits of this test in which specimensare inclined atah angle of 945 and subjected Ito a 20 .sodium ohloridefo at about F. fora number of hours are given in the followin tables.

"TABLE I .Illustrating ithe superiority \of the protection afforded bythe .leadcoating andchemical treatment method of this invention, as illustrated in Example I. over ,priOr art -.coating methods.

Leadalloyponted steeL Steel lead coated and 'chemi- .cally meted {according to this mventwnillxamplc I),

As indicated above, the method of this inventionprovided protection only slightly impaired after .430 hours,zcompared to bad-1y rusted surfaces on lead coated or galvanized sheet.

TABLE II Illustrating the improved protection afforded by the lead coating, chemical treatment and lacquer combination according to this invention as illustrated by Example Ia.

Salt spray test 40 hrs. 430 hrs.

Steel sheet lacquered 100% rust. Steel sheet lead coated and chemically No rust. 5% rust treated (Example I). Steel sheet lead coated, chemically treated do No rust and lacquered (Example Ia). I

Thus the coated treated and lacquered surface showed increased corrosion resistanceover that which would have been expected considering the comparative effects of the lacquer alone and the coating plus chemical treatment above.

TABLE III Illustrating the improved protection afforded by the lead coating chemical treatment and red lead paint combination as illustrated by Example Ib.

Salt spray test 40 hrs. 430 hrs. 1500 hrs.

Steel sheet painted with red no rust 1% rust lead paint. 'Steel sheet lead coated and do 5% rust.

chemically treated (Example I). Steelsheetleadcoated,chemido no rust no rust cally treated and painted with red lead paint (Example It).

The above illustrated the unexpected result obtained in which more than 1500 hours protection The top coat of lacquer, paint or the like may be applied by conventional methods, such as dipping, brushing, or spraying. Its constitution may be determined by characteristics desired. For instance, the lacquer coating is advantageous where parts are to be subsequently soldered since the lacquer need not be removed prior to this operation. Red lead paint is useful where the ultimate in protection is desirable. Other types of paint or surface coating compositions may be used under conditions where their characteristics are important.

Accordingly, as shown by illustrated embodiments, the invention consists of a novel system of protective coatings on iron and steel products, the method being one which includes applying in combination an improved lead alloy coating and a subsequent novel chemical treatment which protects not only the lead alloy coating, but also exhibits a tendency to render passive the exposed iron and steel areas. For best results, suflicient thickness of lead alloy'coating should be present to allow the chemical treatment to effectively exhibit its full protectiveness. The chemical treatment may be considered comparable to an initial corrosion of a lead surface wherein a minute layer of lead is used up in providing an adherent, protective coating which thereafter minimizes further atmospheric attack. As shown by increased corrosion resistance, the chemical treatment eflectively seals the pin holes as well as protects the lead alloys surface, and rusting is minimized and substantially eliminated for long periods of time. This is in contrast to prior art metal coatings on ferrous products which on the one hand, in the case of more corrodible sacrificial coating metals rapidly offer themselves to the environment, and on the other hand. in the case of less corrodible coating metals, which generallycause iron to rust more rapidly at the unprotected nin hole areas.

While this invention has been described and illustrated by the examples shown. it is not intended to be restricted specifically thereto and other modifications and variations may be employed as limited by the following claims.

We claim:

1. Method for protection of a corrodible metal surface which comprises coating said surface with a metal selected from the group consisting of lead and alloys thereof with tin and antimony, said coating being of thickness between about 00002 and 0.001 inch, immersing said coated surface in a solution consisting essentially of an alkali metal hydroxide, an alkali metal sulphate and an alkali metal dichrornate, the proportions of each being not less than 15% and not more than 40% of the total solids content of said solution, and water in amount to produce between about 30 grams and grams of total solids per liter. at a temperature of from about 120 F. to F. for a period of about 10 seconds to 5 minutes, removing said surface from said solution and drying the same.

2. Method for protection of a corrodible metal surface which comprises coating said surface with a lead tin alloy, said coating being of thickness between about 0.0002 and 0.001 inch, immersing said coated surface in a solution consisting essentially of an alkali metal hydroxide, an alkali metal sulphate and an alkali metal dichromate, the proportions of each being not less than 15% and not more than 40% of the total solids content of said solution, and water in amount to produce between about 30 grams and 120 grams of total solids per liter, at a temperature of from about 120 F. to 170 F. for a period of about 10 seconds to 5 minutes, removing said surface from said solution and drying the same.

3. Method for protection of a corrodible metal surface which comprises coating said surface with a lead antimony alloy, said coating being of thickness between about 0.0002 and 0.001 inch, immersing said coated surface in a solution consisting essentially of an alkali metal hydroxide, an alkali metal sulphate and an alkali metal dichromate, the proportions of each being not less than 15% and not more than 40% of the total solids content of said solution, and water in amount to produce between about 30 grams and 120 grams of total solids per liter, at a temperature of from about 120 F. to 170 F. for a period of about 10 seconds to 5 minutes, removing said surface from said solution and drying the same.

4. Method for protection of a corrodible metal 7 sur face which comprises coating saidsimate with ametal selected lfriomztheigrmrp consisting --of lead and alloys thereof with tin and antimony,

said coating being of thiclmess' 'between about 00002 and0001'inch,immersing said-coated sur- .iace :in a solution consisting essentially of an alkali metal hydroxide, an alkali :metal sulphate utes, removing -said surface if rom said solution and drying the same and applying thereon ,a coating of afilm forming and drying surface coating composition.

5. Method for protection of a corrodiblemetal surface which comprises coating said-surface with a metal selected from thegroup consisting of lead and alloys thereof With tin and antimony, said coating being of thickness between about 00002 and 0.001 inch, immersing said coated surfacein a solution consisting essentially of an alkali metal hydroxide, an alkali metal sulphate and an alkali metal dichromate, the proportions of each being not less than 15% and not more than 40% of the total solids content of said solution, and water in amount to produce between about 30 grams and 3 120 grams of total solids per liter, at a temperature of from about 120 F. to 170 F. for a period of about 10 seconds to 5 minutes, removing said surface from said solution and drying the same 8 and applying thereon acoating of red lead paint. 6. .Method for protection of corrodible metal surface whichco'm'prise's coating's'aid surface with ametal selectedtrdmfthe group consisting of lead "andalloys thereof with 'tin and antimony said moving :said surface :from said solution and drying the same and applying thereon a coating -of lacquer.

CARL H. HACK.

GUSTAYE E. BEHR.

GEORGE J. VAHRENKAMP.

REF'ERENCES CITED The fo'llowing references are of record "in the file of this patent:

UNITED STAEES PATENTS Number Name Date 132,746 Berry Nov. 5, 1872 258,082 'Lang hammer l/lay I6, 1882 2,106,904 Wilhelm Feb. 1, 1938 2,132,584 speller Oct. 11, 193 

